Two problems to which vehicle windshield wipers are inevitably subject are wind lift and blade chatter. Wind lift is caused by the exposure of blade support structures to higher speed air streams at higher vehicle speeds, which can catch and lift the blade away from the windshield. This phenomenon becomes worse as windshields become more raked or slanted. In the absence of an anti-lift air foil or some other external wipe force adjustment mechanism, stronger wiper arm springs are necessary to pull the wiper blade more strongly against the glass. Wiper chatter is caused by friction between the blade and the glass as the blade is swept across the windshield surface. Being rubber, the blade is somewhat tacky, and tends to stick to the surface, and is also elastic, tending to stretch as it sticks. When it has stretched enough to overcome the coefficient of friction, the inventors of the subject invention have found, the blade slips and actually bounces or hop up slightly relative to the windshield, before the stick-slip cycle begins again.
Stick-slip has been mentioned in issued U.S. patents, for example, U.S. Pat. No. 4,361,927 to Matsui et al, although it appears that the phenomenon may have been previously understood as a side-to-side, back-and-fourth motion, generally parallel to the plane of the windshield, It does not appear certain that the up-and-down, windshield bouncing motion was recognized. This is indicated by the proposed solution, which is a dumbbell shaped weight pivoted to the blade tip and designed to rattle back and fourth in the direction parallel to the windshield, colliding with the blade support, in opposition to the perceived back-and-forth chatter of the blade. Elastic linears inboard of the weights are intended to absorb the energy of the collision. It is not at all clear that such a device would have any practical effect in stopping the kind of blade bouncing chatter that has been recently analyzed. Moreover, the pivoting mass would be very subject to clogging with dirt, ice, and snow, and would very likely whistle due to exposure to the air stream.
Various air-foil designs exist for counteracting wind lift. These generally consist of an air-foil shaped member attached to the wiper arm and exposed to the air stream. The air-foil shape is oriented so as to push down on the arm at higher speeds. These designs are, of course, not directed at blade chatter.